Question

An electrical firm manufactures light bulbs that have a length life with normal distribution, and a standard deviation of o = 40 hours. A sample of size n = 100 bulbs has an average life of 650 hours. Find the lower 99% confidence bound for the population mean of all bulbs produced by this firm. (use interval notation). What z value(s) did you use to calculate the confidence interval above? Explain why briefly.

Please explain the Z values used.

Answer 1

Given :

$\sigma$ = 40

n = 100

= 650

T

significance level ,

$\alpha$ = 1-99/100

= 0.01

fos confidence inteswar we always used two tall Valve Therefore Zdie = 20.0112 = 2.58 (from 2-table) Lower gylo confidence bound LCB = m - 2212x615m : 650 2.58x 20 Vioo II 639.68